This invention relates to improvements in positive feed drills. More particularly, but not by way of limitation, this invention relates to an improved locking mechanism for ensuring positive feed of the drilling tool and tool holder during operation of the positive feed drill.
This invention is an improvement to the positive feed structure described in detail in U.S. Pat. No. 3,411,385 issued Nov. 19, 1968, to Robert C. Quackenbush. This invention also constitutes an improvement to somewhat similar tools that previously utilized half nuts to engage the feed screw during the drilling operation.
In the apparatus illustrated and described in U.S. Pat. No. 3,411,385, a pressure actuated braking system is illustrated in FIG. 8 that is utilized to lock the shafts carrying gears which engage the external thread on the feed screw to cause axial movement of the feed screw as it rotates in the drill housing. The apparatus of that patent has proved to be extremely successful, but on some occasions, when an extremely hard or tough material is being drilled, or when the drill bit has become dull, the torque imposed by the drill motor sometimes overcomes the braking system and results in stalling or variation of the feed rate of the drilling tool.
Accordingly, an object of this invention is to provide an improved locking mechanism that functions in conjunction with the feed screw, so that the drilling tool feed will not stall nor will the feed rate vary.